The present invention relates to a method of cleaving a brittle material using a point heat source which is capable of providing a thermal stress to the brittle material.
As conventional methods of cutting a brittle material such as semiconductor wafers, ceramic wafers and glass substrates, a dicing method and a scribing method have generally been known. The dicing method is carried out by use of a diamond blade. The scribing method is carried out by forming a crack on a surface of the wafer and then applying a mechanical stress to the wafer to cut the wafer along the scribing lines.
The above conventional methods have disadvantages in cutting the material on which electric circuits are formed. The above conventional methods allow generation of micro-cracks or particles.
In order to solve the above problems with micro-cracks or particles, it was proposed to use a point heat source such as a laser beam for applying a thermal stress to the brittle material to cleave the same. This method is, for example, disclosed in Japanese laid-open patent publication No. 3-13040. This method will be described with reference to FIG. 1. A brittle material 21 is intended to be cleaved along a cleaving line 24. A recess 22 is first formed by use of a mechanical tool at a cleaving starting point which is defined as a crossing point of the cleaving line 24 and one side edge of the brittle material 21. A point heat source is used to locally apply a heat point 23 which is positioned on the cleaving line 24 and in the vicinity of the recess 22 so that a tensile stress is generated in a direction along tangential lines of virtual isothermal lines defined by the heat point 23. For this reason, the tensile stress causes a crack from the recess 22. The crack propagates from a tip of the recess 22 toward the point of the heat point 23. The tip of the crack propagates from the recess 22 toward the point of the heat source 23 so that the crack extends to a position which is close to but distanced from the point of the heat source 23. The crack, however, does not reach the point of the heat source 23 because no tensile stress appears on the point of the heat source 23. The point of the heat source 23 is moved to a point which is distanced from the tip of the crack and also which is positioned on a tangential line of the cleaving line 24 at the tip of the crack, so that the tip of the crack further propagates along the cleaving line 24. Namely, the heat source point 23 is positioned not just on the cleaving line but in the vicinity of the cleaving line 24.
In the above conventional cleaving method using the point heat source, heating conditions such as the position of the heat source 23 and the heating time have been found by trial-and-error method, wherein a distance between the tip of the crack and the point of the heat source 23 as well as a heating time should be varied to determine an optimum heating point and an optimum heating time for effectively and efficiently adding the thermal stress to the crack of the brittle material strip. The optimum heating point and the optimum heating time depend upon the material of the brittle strip and the width thereof. This means that the optimum distance between the tip of the crack and the point of the heat source 23 as well as the optimum heating time depend upon the material of the brittle strip and the width thereof, for which reason the optimum distance between the tip of the crack and the point of the heat source 23 as well as the optimum heating time are required to be found for every different materials of the brittle strip and the different widths thereof. Even if the distance between the tip of the crack and the point of the heat source as well as the heating time are required by the trial-and-error method, then those distance and heating time might be slightly different from the actual optimum distance and heating time. The conventional cleaving work is time-consuming procedure. This makes it difficult to realize automation of the laser beam machining.
In the above circumstances, it had been required to develop a novel method of cleaving a strip of brittle material free from the above problems.